1. Technical Field
This invention is directed towards regenerative heat pump system and method using a working fluid or refrigerant and an adsorbent material.
2. Discussion of the Invention
Heat pumps using solid adsorbent beds are well known as shown by U.S. Pat. Nos. 4,610,148, 4,637,218 4,694,659, 5,025,635, 5,046,319 and 5,079,928. In general since adsorbents take up the working fluid when cooled and desorb the working fluid when heated, adsorbent heat pumps are said to be heat driven. Often in adsorbent heat pumps two beds of sorbents are used, one to adsorb the working fluid while the other bed is desorbing the working fluid. Alternate heating and cooling of the beds is the conventional procedure. When used in air conditioning, heat from an interior room may be used to evaporate the working fluid in an evaporator with heat rejection to the environment at ambient temperatures.
In all of such systems the efficiency of the apparatus is measured by its coefficient of performance or "COP". By the term "COP" as used herein is meant the ratio of heating or cooling work performed divided by the amount of power required to do the work. Since cooling COP.sub.s, or COP.sub.CS, are generally lower than heating COP.sub.S, or COP.sub.HS, many systems are rated on their cooling COP.sub.S.
U.S. Pat. No. 4,637,218 mentions cooling COP.sub.S between 1 and 2 and heating COP.sub.S between 2 and 3. In U.S. Pat. No. 4,637,218 a hot coolant is pumped from a hot 204.4.degree. C. sorbent compressor to a cooler 37.8.degree. C. sorbent compressor, while at the same time cold coolant is pumped from the cooler sorbent compressor to the hotter sorbent compressor. Both compressors exchange heat yielding a typical heat regeneration efficiency of about 80%. The remainder of the heat is supplied by a boiler at about 204.degree. C.
U.S. Pat. No. 4,610,148 reports a theoretical heating COP of about 3 and a cooling COP of about 2, and, a calculated operating COP.sub.H of about 2.6 and a calculated operating COP.sub.C of about 1.6.
FIG. 3 of U.S. Pat. No. 4,694,859, which is concerned with a dual sorbent bed heat pump, shows heating and cooling COP's as a function of a dimensionless thermal wavelength parameter.
Cryogenic cooler systems for sorption refrigerators using a sorption compressor, a heating/cooling loop and a Joule-Thomson expansion valve, or "J-T" valve, with methane as a refrigerant gas and charcoal as the adsorbent, are disclosed in articles entitled "High Efficiency Sorption Refrigerator Design", and, "Design and Component Test Performance of an Efficient 4 W, 130K Sorption Refrigerator" in Advances In Cryogenic Engineering, Vol. 35, Plenum Press, New York, 1990. Desorption occurs at 4.46 MPa (646 psia), i.e. P.sub.H, and adsorption at 0.15 MPa (22 psia), i.e. P.sub.L, or a pressure ratio of about 30, i.e. P.sub.H /P.sub.L =30. Methane is expanded from 4.46 MPa to 0.15 MPa to achieve cooling below 130K. (-143.degree. C.). The sorbent is heated from 240K. (-33.degree. C.) to 600K. (327.degree. C.) to desorb the methane.
A two staged adsorption system is disclosed in an article entitled "Improving Adsorption Cryocoolers By Multi-stage Compression And Reducing Void Volume", Cryogenics, 1986, Vol. 26, page 456, by S. Bard. Refrigerant is passed between carbon adsorbent stages. However, a circuit for the heat transfer fluid for regenerating heat was not shown. It is understood that the heat was simply exhausted and not regenerated.
U.S. Pat. No. 5,025,635 discloses staged adsorbers each containing different adsorbents, i.e. MgBr.sub.2, CoBr.sub.2, CoCl.sub.2, CaBr.sub.2 and SrBr.sub.2 in a single housing.
U.S. Pat. No. 5,079,928 mentions that some reactors in a staged system can be combined into a single reactor.
Regenerative heat transfer fluid circuits for a single stage system are disclosed in U.S. Pat. No. 5,046,319.
Other references of interest are U.S. Pat. Nos. 4,732,008, 4,827,728 and 4,848,994, and an article entitled "Sorption Cooler Technology Development At JPL, Cryogenics, 1990, Vol. 30, page 239, by J. A. Jones.